The characterization of the receptors in mammalian skin is largely complete. In these experiments, it is proposed to trace the activity of cutaneous mechanoreceptors to the first synaptic links in the sensory pathway. Once it has been determined which kinds of receptors excite or inhibit a particular postsynaptic neuron, the characteristics of the relay can be compared with the characteristics of the receptors influencing it. This type of analysis can then be repeated at successively higher levels in the sensory pathway. In this way, it is hoped that some insight can be gained into the way in which information is handled at the first and later synapses of a sensory system. The receptors that signal static limb position are not known. It is proposed to locate these receptors and identify the central pathways that mediate their activity. Once this basic information is available, the properties of the pathways can be analyzed and compared with those relaying activity from cutaneous mechanoreceptors. It is well known that functional recovery is better after a crush injury to a cutaneous nerve than after the nerve has been cut, but the reasons for this difference are not understood. It is also known that some mechanism guides regenerating cutaneous nerve fibers back to the sites in the skin that they formerly innervated. Experiments will be conducted to determine the nature of the guidance mechanism and its relationship to the differing degrees of functional recovery that occur after nerve crush and nerve transection. Thus, it may be possible to gain a greater understanding of the factors responsible for guided nerve growth and the differences in functional recovery after various types of nerve injury.